Reintroduction of Air in Delivery System Accumulator

ABSTRACT

According to one embodiment, an apparatus for reintroducing air includes a bypass valve that reduces pressure in an accumulator that stores reductant to less than an air supply pressure of an air supply. The apparatus also includes a metering valve that fills the accumulator with air from the air supply at the air supply pressure, and a pump that pumps reductant into the accumulator.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application No. 61/788,484, filed Mar. 15, 2013, which is incorporated herein by reference

FIELD

This application relates generally to internal combustion engine systems, and more particularly to reductant delivery systems for exhaust gas after-treatment systems.

BACKGROUND

Typical exhaust after-treatment systems include components that reduce the level of harmful exhaust emissions present in the exhaust gas. Emission requirements vary according to engine type. For example, emissions tests for compression-ignited engines (e.g., diesel-powered engines) typically monitor the concentration of carbon monoxide, nitrogen oxides (NOx), and unburned hydrocarbons (UHC) that are released from the tail-pipe to make sure that the concentrations of such compounds leaving the tail-pipe are within certain emissions standards. An exhaust after-treatment system may employ selective catalytic reduction (SCR) components to convert NOx to Nitrogen and other compounds.

Conventional exhaust after-treatment systems utilize a reductant, typically a diesel exhaust fluid (DEF), such as aqueous urea, ammonia, and the like as a reagent to reduce the NOx in the exhaust gas. The reductant is dosed into an exhaust gas stream to convert the harmful emissions. The exhaust after-treatment system may employ a reductant delivery system with an accumulator and pressurized air to deliver pressurized reductant for dosing the exhaust gas. Air within the accumulator may stabilize the pressure of the reductant. Unfortunately, during dosing the air may migrate from the accumulator.

SUMMARY

The subject matter of the present application has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available exhaust after-treatment systems. Accordingly, the subject matter of the present application has been developed to provide an apparatus, method, and system for reintroducing air into a reductant delivery system accumulator.

According to one embodiment, an apparatus for reintroducing air includes a bypass valve that reduces pressure in an accumulator that stores reductant to less than an air supply pressure of an air supply. The apparatus also includes a metering valve that fills the accumulator with air from the air supply at the air supply pressure, and a pump that pumps reductant into the accumulator.

In some implementations of the apparatus, the bypass valve reduces pressure in the accumulator to less than the air supply pressure of the air supply in response to a timer exceeding a predetermined threshold. The predetermined threshold can include an upper pressure threshold and a lower pressure threshold. The timer will increment when the pressure in the accumulator is more than the upper pressure threshold or the pressure in the accumulator is less than the lower pressure threshold. In certain implementations, the upper pressure threshold is associated with a first predetermined percentage of a target pressure greater than the target pressure, and the lower pressure threshold is associated with a second predetermined percentage of a target pressure lower than the target pressure. The first and second predetermined percentages can be between about 10% and 30%

According to certain implementations of the apparatus, the bypass valve reduces pressure in the accumulator to less than the air supply pressure of the air supply in response to the expiration of a priming time interval. The priming time interval can be between about 4 hours and about 16 hours.

In some implementations, the bypass valve reduces pressure in the accumulator by opening to allow reductant in the accumulator to drain from the accumulator. Further, the metering valve may close to prevent filling the accumulator with air from the air supply while the bypass valve is opened. Additionally, the pump can stop pumping reductant into the accumulator while the bypass valve is open and when the metering valve is filling the accumulator with air.

According to another embodiment, an internal combustion engine system includes an internal combustion engine and an exhaust after-treatment system that treats exhaust gas from the internal combustion engine. The engine system further includes a reductant delivery system that provides reductant to the exhaust after-treatment system. The reductant delivery system also includes a reductant source, an accumulator that stores reductant, and a bypass valve downstream of the accumulator and upstream of the reductant source. The bypass valve is operable to reduce pressure in the accumulator to less than an air supply pressure of an air supply downstream of the bypass valve. The reductant delivery system further includes a metering valve downstream of the accumulator and the bypass valve and upstream of the air supply. The metering valve is operable to fill the accumulator with air from the air supply at the air supply pressure. Additionally, the reductant delivery system includes a pump downstream of the reductant source and upstream of the accumulator. The pump is operable to pump reductant from the reductant source into the accumulator.

In some implementations, the internal combustion engine further includes a controller that monitors a pressure within the accumulator, and stops the pump, closes the metering valve, and opens the bypass valve when a magnitude of pressure oscillations within the accumulator meets a threshold. A timer increments when the pressure in the accumulator is more than an upper pressure threshold or the pressure in the accumulator is less than a lower pressure threshold. The magnitude of pressure oscillations may be determined using the timer. The engine system may further include a reductant nozzle that injects reductant into the exhaust gas from the internal combustion engine. The controller may close the bypass valve and open the metering valve after reductant has drained from the accumulator through the bypass valve. In some implementations, the controller closes the metering valve and starts the pump when the pressure within the accumulator is equal to or less than the air supply pressure.

According to yet another embodiment, a method for reintroducing air includes reducing pressure in an accumulator storing reductant to less than an air supply pressure of an air supply. The method also includes filling the accumulator with air at the air supply pressure through a metering valve connecting the accumulator to the air supply. Additionally, the method includes pumping reductant into the accumulator from a pump.

In some implementations, the method includes detecting an air volume in the accumulator, stopping the pump in response to the detected air volume indicating a low air volume, closing the metering valve in response to the detected air volume indicating a low air volume, and opening a bypass valve to drain reductant from the accumulator in response to stopping the pump and closing the metering valve. The method may include closing the bypass valve after reductant has been drained from the accumulator. Additionally, the method may include opening the metering valve after reductant has been drained from the accumulator, supplying air at the air supply pressure to the accumulator through the metering valve after reductant has been drained from the accumulator until pressure within accumulator reaches the air supply pressure, closing the metering valve after the air pressure within the accumulator reaches the air supply pressure, and pumping reductant into the accumulator from the pump after the accumulator reaches the air supply pressure and the metering valve is closed.

Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the subject matter of the present disclosure should be or are in any single embodiment. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present disclosure. Thus, discussion of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment.

The described features, structures, advantages, and/or characteristics of the subject matter of the present disclosure may be combined in any suitable manner in one or more embodiments and/or implementations. In the following description, numerous specific details are provided to impart a thorough understanding of embodiments of the subject matter of the present disclosure. One skilled in the relevant art will recognize that the subject matter of the present disclosure may be practiced without one or more of the specific features, details, components, materials, and/or methods of a particular embodiment or implementation. In other instances, additional features and advantages may be recognized in certain embodiments and/or implementations that may not be present in all embodiments or implementations. Further, in some instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the subject matter of the present disclosure. The features and advantages of the subject matter of the present disclosure will become more fully apparent from the following description and appended claims, or may be learned by the practice of the subject matter as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the subject matter may be more readily understood, a more particular description of the subject matter briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the subject matter and are not therefore to be considered to be limiting of its scope, the subject matter will be described and explained with additional specificity and detail through the use of the drawings, in which:

FIG. 1 is a schematic block diagram illustrating one embodiment of an internal combustion engine system;

FIG. 2 is a schematic block diagram illustrating one embodiment of a reductant delivery system;

FIG. 3 is a flow chart diagram illustrating one embodiment of a method for reintroducing air; and

FIG. 4 is a chart illustrating one embodiment of reintroducing air.

DETAILED DESCRIPTION

FIG. 1 is a schematic block diagram illustrating one embodiment of an internal combustion engine system 190. The system 190 includes an internal combustion engine 195, an exhaust after-treatment system 180, and a reductant delivery system 100. The internal combustion engine 195 combusts fuel, producing mechanical energy and exhaust gas. The exhaust gas includes components such as NOX that are harmful to the environment. As a result, the system 100 converts these components into less harmful byproducts.

The exhaust gas is treated by the exhaust after-treatment system 180. In one embodiment, the exhaust after-treatment system 180 douses the exhaust gas with a reductant. The reductant may be a diesel exhaust fluid (DEF). The reductant delivery system 100 may supply the reductant to the exhaust after-treatment system 180.

FIG. 2 is a schematic block diagram illustrating one embodiment of the reductant delivery system 100. The system 100 includes a reductant tank 110, a pump 115, an accumulator 120, a metering valve 130, an air supply 125, a controller 155, and a nozzle 160.

The reductant tank 110 stores reductant and provides reductant to the pump 115. The reductant in the reductant tank 110 may be at an input pressure P_(in) 140. In one embodiment, P_(in) 140 is ambient pressure. The pump 115 pumps the reductant into the accumulator 120. The pump 115 may pump the reductant at a first pressure P₁ 145. The first pressure 145 may be in the range of 450 to 650 kilopascals (kPa). In one embodiment, a target first pressure 145 is 500 kPa.

The accumulator 120 is primed with air. The air resides in an upper portion of a cavity within the accumulator 120 as is well known to those of skill in the art. The reductant enters and exits the accumulator 120 through ports that are below the level of the air. As a result, the air is prevented from flowing directly out of port.

The metering valve 130 meters the reductant from the accumulator 120 to the nozzle 160. The reductant may be mixed with pressurized air from the air supply 125. The air supply pressure P₂ 150 of the air supply 125 may be in the range of 350 to 450 kPa. In one embodiment, the air supply pressure 150 may be 400 kPa. The nozzle 160 may dose the exhaust gas with the reductant. The air supply 125 may be a brake air supply. A pressure sensor 175 may measure the air supply pressure P₂ 150 of the air supply 125. The pressure sensor 175 may communicate a pressure value to the controller 155.

The bypass valve 135 may open to allow reductant to flow from the accumulator 122 the reductant tank 110. The bypass valve 135 and the metering valve 130 may open and close in response to commands from the controller 155. The controller 155 may control the operation of the pump 115, and the opening and closing of the metering valve 130 and the bypass valve 135. In addition, the controller 155 may receive pressure values from the pressure sensors 170, 175.

The controller 155 may include a processor and a computer readable storage medium. The computer readable storage medium may store computer readable program code. The processor may execute the computer readable program code to perform the functions of the controller 155.

The accumulator 120 stabilizes the first pressure 145 of the reductant. When the first pressure 145 increases, such as when the metering valve 130 is closed, the air is compressed, dampening the increase in the first pressure 145. Similarly, when the first air pressure 145 decreases, such as when the metering valve 130 is opened, the air in the accumulator 120 expands, dampening the decrease in the first pressure 145. The pressure sensor 170 may measure the first pressure 145.

In one embodiment, the metering valve 130 precisely meters the reductant to ensure that the exhaust gas is not dosed with insufficient reductant or that too much reductant is not applied. Yet the reductant cannot be precisely metered if the first pressure 145 oscillates significantly. As a result, the air in the accumulator 120 dampens the first pressure 145 so that the reductant can be metered more precisely.

Unfortunately, although the air cannot flow directly out of the ports of the accumulator 120, the air does dissolve into the reductant and flow out of the accumulator 120 with the reductant. As a result, over time the volume of air in the accumulator 120 decreases. For example, the air in accumulator 120 may have insufficient volume to dampen the first air pressure 145 after 8 to 12 hours of operation of the internal combustion engine system 190.

When there is insufficient air in the accumulator 120, oscillations of the first pressure 145 increase. As a result, the metering of the reductant from the metering valve 130 to the nozzle 160 is less precise.

The accumulator 120 could be re-primed with air from a dedicated, pressurized priming air line. However, the addition of such a dedicated air line along with the required valves, controls, and air supply may increase the cost and reduce the reliability of the accumulator 120. The embodiments described herein reintroduce air into the accumulator 120 without a dedicated priming line. As a result, the accumulator 120 may be regularly re-primed with air as will be described hereafter. In one embodiment, the reintroduction of the air is performed by an apparatus 175 made up of the pump 115, the accumulator 120, the metering valve 130, the bypass valve 135, and the controller 155.

FIG. 3 is a flow chart diagram illustrating one embodiment of a method 500 for reintroducing air. The method 500 may be performed by the apparatus 175, the reductant delivery system 100, and the internal combustion engine system 190. In one embodiment, the controller 155 controls functions of the pump 115, the metering valve 130, and the bypass valve 135 to perform the method 150.

The method 500 starts, and in one embodiment the controller 155 detects 502 the air volume in the accumulator 120. The controller 155 may detect 502 the air volume based on oscillations in the first pressure 145. The controller 155 may record pressure values from the pressure sensor 170. In some implementations, the controller 155 may record the oscillations in the first pressure 145 using a timer or counter. When the first pressure 145 exceeds an upper pressure threshold or when the first pressure falls below a lower pressure threshold, the timer or counter is incremented. If the pressure oscillations, as indicated by the timer or counter, exceed a threshold, the controller 155 may detect 502 a low air volume condition as will be described hereafter.

The pressure threshold may be in the range of 10 to 30 percent greater than or less than a target pressure. For example, if the target pressure for the first pressure 145 is 500 kPa, the pressure threshold may be plus and minus 10 percent of the target pressure, or plus and minus 150 kPa.

In one embodiment, the controller 155 detects 502 the air volume in the accumulator 120 in response to a priming time interval expiring. The priming time interval may be in the range of 4 to 16 hours. In a certain embodiment, the priming time interval is in the range of 6 to 10 hours. For example, if the priming time interval is eight hours, the controller 155 may detect 502 the air volume every eight hours.

In one embodiment, the controller 155 stops 504 the pump 115. Thus the pump 115 does not pressurize the reductant in the accumulator 122 to the first pressure 145. In addition, the controller 155 may close the metering valve 130.

The bypass valve 135 may reduce 506 the first pressure 145 in the accumulator 120. In one embodiment, the controller 155 opens the bypass valve 135, allowing the reductant in the accumulator 120 to flow from the accumulator 120 into the reductant tank 110 to reduce 506 the first pressure 145. The bypass valve 135 may reduce 506 the first pressure 145 until the first pressure 145 is less than the air supply pressure 150. In one embodiment, the reductant drains from the accumulator 120 into the reductant tank 110.

The bypass valve 135 may close 508 in response to a command from the controller 155. The controller 155 may only close 508 the bypass valve 135 if the first pressure 145 is less than the air supply pressure 150. In one embodiment, the controller 155 closes 508 the bypass valve 135 if the first pressure 145 is a pressure difference less than the air supply pressure 150. The pressure difference may be in the range of 5 to 25 percent of the air supply pressure 150.

The metering valve 130 may open 510. In one embodiment, the controller 155 opens 510 the metering valve 130 if the bypass valve 135 is closed and if the first pressure 145 is less than the air supply pressure 150.

The metering valve 130 may fill 512 the accumulator 120 with air from the air supply 125 at the air supply pressure 150. In one embodiment, the metering valve 130 opens to fill 512 the accumulator 124 for a specified reintroduction time interval. The reintroduction time interval may be in the range of 2 to 20 seconds. Because the air supply pressure 150 is greater than the first pressure 145, the air flows through the metering valve 130 and into the accumulator 120.

In one embodiment, the controller 155 closes 514 the metering valve 130 after the expiration of the reintroduction time interval. Alternatively, the controller 155 closes 514 the metering valve 130 when the first pressure 145 is equal to the air supply pressure 150.

The pump 115 may pump 516 reductant into the accumulator 120 and the method 500 ends. Some of the air in the accumulator 120 remains when the reductant is pumped into the accumulator 120 and is pressurized to the first pressure 145. Thus air is reintroduced to the accumulator 120 and the accumulator 120 has sufficient air volume to effectively dampen oscillations of the first pressure 145.

FIG. 4 is a chart 200 illustrating one embodiment of reintroducing air. The chart 200 shows the first pressure 145 of the reductant and the air supply pressure 150 of the mix of reductant and pressurized air that is fed to the nozzle 160. The chart 200 also depicts the transitions of the bypass valve 135 and the metering valve 130 between open and closed positions.

As depicted, the metering valve 130 opens to supply reductant to the nozzle 160. When the air volume of the accumulator 120 is low, as shown in seconds 100 to 190, the accumulator 120 does not sufficiently reduce the oscillations 225 of the first pressure 145 as the metering valve 130 opens to release reductant and closes to retain reductant.

In the depicted embodiment, the oscillations 225 of the first pressure 145 exceed a pressure threshold range defined by upper and lower thresholds 220 a, 220 b. The controller 155 may determine from the oscillations of the first pressure 145 exceeding the pressure threshold 220 that the air volume within the accumulator 120 is low. The controller 155 may use a timer or counter that increments each time the first pressure 145 exceeds or falls below the upper and lower thresholds 220 a, 220 b. Once the timer or counter meets or exceeds a threshold value, a low air volume condition may be detected for the accumulator 120. In response to detecting the low air volume in the accumulator 120, the controller 155 may close 205 the metering valve 130. In addition, the controller 155 may stop the pump 115.

The bypass valve 135 opens 210 to reduce the first pressure 145. In one embodiment, the controller 155 opens the bypass valve 135 until the first pressure 145 is less than 215 the air supply pressure 150. The controller 155 may further close 211 the bypass valve 135 when the first pressure 145. In one embodiment the controller 155 closes 211 the bypass valve 135 when the first pressure 145 is less than 215 the air supply pressure 150.

The metering valve 130 fills the accumulator 120 with air from the air supply 125 at the air supply pressure 150. The controller 155 may open the metering valve 130 if the first pressure 145 is less than 215 the air supply pressure 150. Because the air supply pressure 150 is greater than the first pressure 145, air flows from the air supply 125 through the metering valve 130 into the accumulator 120, reintroducing air into the accumulator 120.

The controller 155 closes 235 the metering valve 130. The controller 155 may close 235 the metering valve 130 after the expiration of the reintroduction time interval. Alternatively, the controller 155 may close 235 the metering valve 130 when the first pressure 145 is equal to the air supply pressure 150.

The pump 115 pumps 240 the reductant into the accumulator 120 at the first pressure 145, with the first pressure 145 stabilizing near a target pressure. Because the accumulator 120 has been re-primed with air, when the metering valve 130 resumes opening 245, the oscillations 255 of the first pressure 145 are greatly reduced.

By reintroducing air into the accumulator 120, the embodiments mitigate the depletion of air from the accumulator 120 as the air is dissolved into the reductant and removed from the accumulator 120. As a result, the accumulator 120 stabilizes the first pressure of the reductant and the reductant delivery system 100 more precisely supplies the reductant to the nozzle 160 and the exhaust after-treatment system 180. The exhaust after-treatment system 180 operates more efficiently, reducing environmental pollutants. In addition, by reducing peaks of the first pressure 145, components operate within design pressure ranges and are less susceptible to wear and failure.

The schematic flow chart diagrams and method schematic diagrams described above are generally set forth as logical flow chart diagrams. As such, the depicted order and labeled steps are indicative of representative embodiments. Other steps, orderings and methods may be conceived that are equivalent in function, logic, or effect to one or more steps, or portions thereof, of the methods illustrated in the schematic diagrams.

Additionally, the format and symbols employed are provided to explain the logical steps of the schematic diagrams and are understood not to limit the scope of the methods illustrated by the diagrams. Although various arrow types and line types may be employed in the schematic diagrams, they are understood not to limit the scope of the corresponding methods. Indeed, some arrows or other connectors may be used to indicate only the logical flow of a method. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of a depicted method. Additionally, the order in which a particular method occurs may or may not strictly adhere to the order of the corresponding steps shown.

Many of the functional units described in this specification have been labeled as functions, in order to more particularly emphasize their implementation independence. For example, a function may be implemented as a hardware circuit comprising custom VLSI circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. A function may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like.

Functions may also be implemented in software for execution by various types of processors. An identified function of executable code may, for instance, comprise one or more physical or logical blocks of computer instructions, which may, for instance, be organized as an object, procedure, or function. Nevertheless, the executables of an identified function need not be physically located together, but may comprise disparate instructions stored in different locations which, when joined logically together, comprise the function and achieve the stated purpose for the function.

Indeed, a function of computer readable program code may be a single instruction, or many instructions, and may even be distributed over several different code segments, among different programs, and across several memory devices. Similarly, operational data may be identified and illustrated herein within functions, and may be embodied in any suitable form and organized within any suitable type of data structure. The operational data may be collected as a single data set, or may be distributed over different locations including over different storage devices, and may exist, at least partially, merely as electronic signals on a system or network. Where a function or portions of a function are implemented in software, the computer readable program code may be stored and/or propagated on in one or more computer readable storage medium(s).

The computer readable medium may be a tangible computer readable storage medium storing the computer readable program code. The computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, holographic, micromechanical, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing.

More specific examples of the computer readable medium may include but are not limited to a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a portable compact disc read-only memory (CD-ROM), a digital versatile disc (DVD), an optical storage device, a magnetic storage device, a holographic storage medium, a micromechanical storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, and/or store computer readable program code for use by and/or in connection with an instruction execution system, apparatus, or device.

The computer readable medium may also be a computer readable signal medium. A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electrical, electro-magnetic, magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport computer readable program code for use by or in connection with an instruction execution system, apparatus, or device. Computer readable program code embodied on a computer readable signal medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, Radio Frequency (RF), or the like, or any suitable combination of the foregoing

In one embodiment, the computer readable medium may comprise a combination of one or more computer readable storage mediums and one or more computer readable signal mediums. For example, computer readable program code may be both propagated as an electro-magnetic signal through a fiber optic cable for execution by a processor and stored on RAM storage device for execution by the processor.

Computer readable program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The computer readable program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. Similarly, the use of the term “implementation” means an implementation having a particular feature, structure, or characteristic described in connection with one or more embodiments of the present disclosure, however, absent an express correlation to indicate otherwise, an implementation may be associated with one or more embodiments.

In the above description, certain terms may be used such as “up,” “down,” “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,” and the like. These terms are used, where applicable, to provide some clarity of description when dealing with relative relationships. But, these terms are not intended to imply absolute relationships, positions, and/or orientations. For example, with respect to an object, an “upper” surface can become a “lower” surface simply by turning the object over. Nevertheless, it is still the same object. Further, the terms “including,” “comprising,” “having,” and variations thereof mean “including but not limited to” unless expressly specified otherwise. An enumerated listing of items does not imply that any or all of the items are mutually exclusive and/or mutually inclusive, unless expressly specified otherwise. The terms “a,” “an,” and “the” also refer to “one or more” unless expressly specified otherwise.

Additionally, instances in this specification where one element is “coupled” to another element can include direct and indirect coupling. Direct coupling can be defined as one element coupled to and in some contact with another element. Indirect coupling can be defined as coupling between two elements not in direct contact with each other, but having one or more additional elements between the coupled elements. Further, as used herein, securing one element to another element can include direct securing and indirect securing. Additionally, as used herein, “adjacent” does not necessarily denote contact. For example, one element can be adjacent another element without being in contact with that element.

As used herein, the phrase “at least one of”, when used with a list of items, means different combinations of one or more of the listed items may be used and only one of the items in the list may be needed. The item may be a particular object, thing, or category. In other words, “at least one of” means any combination of items or number of items may be used from the list, but not all of the items in the list may be required. For example, “at least one of item A, item B, and item C” may mean item A; item A and item B; item B; item A, item B, and item C; or item B and item C. In some cases, “at least one of item A, item B, and item C” may mean, for example, without limitation, two of item A, one of item B, and ten of item C; four of item B and seven of item C; or some other suitable combination.

The present disclosure may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the disclosure is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. 

1. An apparatus for reintroducing air, comprising: a bypass valve downstream of an accumulator for reducing pressure in the accumulator storing reductant to less than an air supply pressure of an air supply; a metering valve filling the accumulator with air from the air supply at the air supply pressure; and a pump pumping reductant into the accumulator.
 2. The apparatus of claim 1, wherein the bypass valve reduces pressure in the accumulator to less than the air supply pressure of the air supply in response to a timer exceeding a predetermined threshold.
 3. The apparatus of claim 2, wherein the predetermined threshold comprises an upper pressure threshold and a lower pressure threshold, and the timer increments when the pressure in the accumulator is more than the upper pressure threshold or the pressure in the accumulator is less than the lower pressure threshold.
 4. The apparatus of claim 3, wherein the upper pressure threshold is associated with a first predetermined percentage of a target pressure greater than the target pressure, and the lower pressure threshold is associated with a second predetermined percentage of a target pressure lower than the target pressure.
 5. The apparatus of claim 4, wherein the first and second predetermined percentages are between about 10% and about 30%.
 6. The apparatus of claim 1, wherein the bypass valve reduces pressure in the accumulator to less than the air supply pressure of the air supply in response to an expiration of a priming time interval.
 7. The apparatus of claim 6, wherein the priming time interval is between about 4 hours and about 16 hours.
 8. The apparatus of claim 1, wherein the bypass valve reduces pressure in the accumulator by opening to allow reductant in the accumulator to drain from the accumulator.
 9. The apparatus of claim 8, wherein the metering valve closes to prevent filling the accumulator with air from the air supply while the bypass valve is opened.
 10. The apparatus of claim 9, wherein the pump stops pumping reductant into the accumulator while the bypass valve is open and when the metering valve is filling the accumulator with air.
 11. An internal combustion engine system, comprising: an internal combustion engine; an exhaust after-treatment system treating exhaust gas from the internal combustion engine; a reductant delivery system providing reductant to the exhaust after-treatment system and comprising: a reductant source; an accumulator storing reductant; a bypass valve downstream of the accumulator and upstream of the reductant source, the bypass valve operable to reduce pressure in the accumulator to less than an air supply pressure of an air supply downstream of the bypass valve; a metering valve downstream of the accumulator and the bypass valve and upstream of the air supply, the metering valve being operable to fill the accumulator with air from the air supply at the air supply pressure; and a pump downstream of the reductant source and upstream of the accumulator, the pump being operable to pump reductant from the reductant source into the accumulator.
 12. The internal combustion engine system of claim 11, further comprising a controller monitoring a pressure within the accumulator, and stopping the pump, closing the metering valve, and opening the bypass valve when a magnitude of pressure oscillations within the accumulator meets a threshold.
 13. The internal combustion engine system of claim 12, wherein a timer increments when the pressure in the accumulator is more than an upper pressure threshold or the pressure in the accumulator is less than a lower pressure threshold, and the magnitude of pressure oscillations is determined using the timer.
 14. The internal combustion engine system of claim 12, further comprising a reductant nozzle injecting reductant into the exhaust gas from the internal combustion engine.
 15. The internal combustion engine system of claim 12, wherein the controller closes the bypass valve and opens the metering valve after reductant has drained from the accumulator through the bypass valve.
 16. The internal combustion engine system of claim 15, wherein the controller closes the metering valve and starts the pump when the pressure within the accumulator is equal to or less than the air supply pressure.
 17. A method for reintroducing air, comprising: reducing pressure in an accumulator storing reductant to less than an air supply pressure of an air supply via a bypass valve downstream of the accumulator; filling the accumulator with air at the air supply pressure through a metering valve connecting the accumulator to the air supply; and pumping reductant into the accumulator from a pump.
 18. The method of claim 17, further comprising: detecting an air volume in the accumulator; stopping the pump in response to the detected air volume indicating a low air volume; closing the metering valve in response to the detected air volume indicating a low air volume; and opening the bypass valve to drain reductant from the accumulator in response to stopping the pump and closing the metering valve.
 19. The method of claim 18, further comprising closing the bypass valve after reductant has been drained from the accumulator.
 20. The method of claim 19, further comprising: opening the metering valve after reductant has been drained from the accumulator; supplying air at the air supply pressure to the accumulator through the metering valve after reductant has been drained from the accumulator until the air pressure within accumulator reaches the air supply pressure; closing the metering valve after the air pressure within the accumulator reaches the air supply pressure; and pumping reductant into the accumulator from the pump after the accumulator reaches the air supply pressure and the metering valve is closed. 